Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Arsenic, symbol As, extremely poisonous semimetallic element. The atomic number of arsenic is 33. Arsenic is in group 15 (or Va) of the periodic table.

Chemically, arsenic is intermediate between metals and nonmetals. Its properties lie, in general, in the middle of the series formed by the family of the elements nitrogen, phosphorus, arsenic, antimony, and bismuth. Arsenic ranks about 52nd in natural abundance among the elements in crustal rocks. When arsenic is heated, it sublimes, passing directly from solid to gaseous form at 613° C (1135° F). A common form of arsenic is gray, metallic in appearance, and has a specific gravity of 5.7. A yellow, nonmetallic form also exists and has a specific gravity of 2.0. The atomic weight of arsenic is 74.9216.

Arsenic is used in large quantities in the manufacture of glass to eliminate a green color caused by impurities of iron compounds. A typical charge in a glass furnace contains 0.5 percent of arsenic trioxide. Arsenic is sometimes added to lead to harden it and is also used in the manufacture of such military poison gases as lewisite and adamsite. Until the introduction of penicillin, arsenic was of great importance in the treatment of syphilis. In other medicinal uses, it has been displaced by sulfa drugs or antibiotics. Lead arsenate, calcium arsenate, and Paris green are used extensively as insecticides. Certain arsenic compounds, such as gallium arsenide (GaAs), are used as semiconductors. GaAs is also used as a laser material. Arsenic disulfide (As2S2), also known as red orpiment and ruby arsenic, is used as a pigment in the manufacture of fireworks and paints.